Shorter trawls improve size selection of northern shrimp

Abstract

Discards of small northern shrimp (Pandalus borealis) are a problem in the Skagerrak northern shrimp trawl fishery. To reduce catches of small shrimp, we studied the effect of trawl belly length on size selectivity in November 2017 and June 2018 onboard 15 and 27 m double-rigged shrimp trawlers. The selectivity of the vessels’ standard trawl was compared with a trawl differing only in the belly length, being 37% shorter. The trawls had 40 mm bottom panels and cod ends of 35 mm mesh sizes. Eleven and 14 hauls were made, respectively, in 2017 aboard the 15 m vessel and in 2018 aboard the 27 m vessel. The trawls fished shrimp above 19 mm carapace length equally, while catch rates of shrimp below 15.5–16 mm carapace length in the shorter trawl were more than halved. The results were consistent between the two vessels. In short, modifying trawl length is a simple design modification that can reduce catches of small shrimp. Bycatch of Norway pout (Trisopterus esmarkii) was slightly reduced in the shorter trawl, unrelated to fish length.